In a semiconductor integrated circuit device, a silicon nitride film is widely used not only as an insulating material such as a gate insulating film or the like but also as a material such as an etching stopper, a sidewall spacer, a stress liner or the like.
A chemical vapor deposition method (CVD method) has been widely used for such a silicon nitride film forming process. In recent years, with the progress of miniaturization and high integration of semiconductor devices, from the viewpoint of improving characteristics such as an insulation property and the like, attention has been paid to an atomic layer deposition method (ALD method) capable of forming a high-quality film at a lower temperature than the film formation using the conventional CVD method.
As a technique for forming a silicon nitride film by the ALD method, there has been proposed a technique in which a dichlorosilane (DCS; SiH2Cl2) gas, which is a Si source gas, and an ammonia (NH3) gas, which is a nitriding gas, are used and supplied alternately. When supplying the NH3 gas, high-frequency power is applied to generate plasma, thereby promoting a nitriding reaction.
Although a high-quality silicon nitride film can be obtained by the ALD method, there is a growing demand for a dry etching resistance in the silicon nitride film. It is difficult to obtain a sufficient dry etching resistance in a silicon nitride film produced by a conventional ALD method.